1. Field of the Invention
The present invention relates to a device for machining workpieces, more particularly workpieces of wood-based materials, plastics or the like. invention relates furthermore to a method of machining workpieces by means of such a device.
2. Prior Art
Known from DE 195 09 933 C1 is a chip removing, rotating tool for machining workpieces, more particularly workpieces of wood-based materials, plastics or the like, which is configured substantially as a hollow body and comprises at least one cutter at its outer circumference. A portion of the tool adjoining each cutter is penetrated by a chip receiving opening for communicating the chips into a cavity, namely a quill shaft of the tool, i.e. the tool featuring internal chip removal. To assist removal of the chips materializing in operation of this tool it is possible to pass an air stream longitudinally, i.e. axially, through the quill shaft of the tool. Furthermore evident from this reference document is that chip removal may be additionally assisted by a conical configuration of the quill shaft of the tool.
In devices including the type of tool as described above a very high proportion of the resulting chips gains access to the cavity within the tool. Where wood-based materials are concerned, this proportion may be as high as approx. 95% to approx. 98% of the resulting chips.
Accordingly, chip removal or chip exhaust from the tool is especially of importance.
Experience has shown, however, that in conventional devices comprising tools with internal chip removal the chips can only be exhausted at a very high energy expense. For example, the energy requirement for such exhaust systems in woodworking operations is on an average between approx. 30% and approx. 50% of total electrical power consumption per year. This is why it would be desirable and good practice from both a technical and costeffective consideration to reduce the energy consumption for such exhaust systems.
In tools incorporating internal chip removal, a chip separated from the workpiece is usually accelerated by the cutter and moves through the chip receiving opening into the tool cavity. Due to the tool rotating, the air mass accommodated in the cavity is exposed to a centrifugal effect, however, as a result of which the entrained air tends to emerge outwardly from the chip receiving opening, i.e. the air mass flows in a direction which is precisely opposite to the direction of movement or trajectory of the chips entering the tool. This obstructs the movement of the chips into the tool cavity and the chips are decelerated or even directed back out of the chip receiving opening, it being particularly large chips that suffer from this disadvantageous effect. It is these unwanted effects that may result in chip removal being detrimented or even in the chip receiving opening becoming blocked which aggravates tool wear. Chips having regained access to the outer side of the tool or chips failing to be handled by the chip receiving opening and/or exhaust may, in addition, be multiply cut unnecessarily at the machining site of the tool, this likewise aggravating tool wear, resulting in reduced tool life and, last-but-not-least, in higher pollution of the ambient air.
In addition, chips having gained access to the tool cavity, but greatly decelerated are forced outwardly by the centrifugal force against the inner wall the tool cavity where they may accumulate and even become cemented. This substantially hampers chip removal and may even result in the tool becoming unbalanced which particularly at high tool rotating speeds is detrimental to operational safety.
Chips which are not removed and/or even regain access to the chip receiving opening may in addition accumulate or build up at the surface of the workpiece and cause undesirable chip marks, it being particularly multiply cut chips that result in ugly marking of the workpiece where softish materials are concerned, such as, for example, wood-based materials or plastics. This results in a reduction in workpiece quality which is, of course, undesirable.
This is why devices of the aforementioned kind equipped with tools, having internal chip guidance, require for satisfactory chip removal external high-power exhaust means for high exhaust velocities especially for high cutting speeds and rotary speeds, resulting, however, not only in a corresponding high power requirement but also causing a noise nuisance due to such exhaust systems.
However, the type of tool used as such has also proven to be a considerable source of noise. Thus, conventional tools, having internal chip removal, generate high noise emissions involving screeching and/or pulsating acoustic oscillations experienced by operators of the device to be extremely unpleasant, it thus also being desirable to reduce the noise emission produced by the device including its tools.
The objective or the technical problem forming the basis of the present invention is to provide a suitable device and a suitable method for machining workpieces which permit improved chip removal for a lower exhaust capacity and a reduced noise emission.
This technical problem is solved by a device in accordance with the invention having the features of claim 1.
This device for machining workpieces, more particularly workpieces of wood-based materials, plastics or the like comprises
at least one chip removing, rotating tool configured substantially as a hollow body including at least one cutter, a portion of the tool adjoining the cutter being penetrated by a chip receiving opening for communicating chips into a tool cavity; and
an exhaust means including a stationary exhaust housing configured substantially as a hollow body communicating with or protruding into the tool cavity at least in part and in connection with at least one exhaust air source;
the portion of the exhaust housing communicating with the tool cavity comprising in the region of an effective site of the tool assigned to the cutter at least one chip communicating window porting into an exhaust passage of the exhaust housing; and
the exhaust passage comprising in an exhaust passage section upstream of the chip communicating window, relative to the exhaust direction, at least one auxiliary air infeed opening.
The tool of the device in accordance with the invention, which is to be classified as a tool having internal chip removal, may be configured one-part or multi-part. A multi-part tool may comprise, for example, a one-part or multi-part thin-walled quill body for connecting to a tool shaft or spindle and/or other components of the tool. The tool is formed preferably rotationally symmetrical, although the invention is not restricted to this configuration, however.
The at least one cutter of the tool, which may be a geometrically defined, straight, profiled or regular or irregular shaped cutter may be an integral part of the tool or, however, a separate part of the tool. The cutter may be configured more particularly interchangeable, the tool in this case expediently featuring a suitable quick-change means. The number of tool cutters depends on the application in each case.
Instead of a single cutter, it is, of course, just as possible that two or more cutters find application. The cutters are preferably applied to the radial outer circumference of the tool. However, the tool may also comprise in addition facing cutters.
The exhaust housing may be one-part or multi-part. As already mentioned above, the exhaust housing is arranged stationary. More particularly, the part of the exhaust housing communicating with or protruding into the tool cavity at least in part may be adjustable as regards its stationary arrangement, however. The part of the exhaust housing communicating with or protruding into the tool cavity is preferably formed rotationally symmetrical at its sections located opposite the inner wall the tool cavity. It is, however, expressly to be noted that the invention is not restricted to this configuration. The part communicating with the cavity may also be configured asymmetrical or irregular, or comprise irregularly shaped sections. The exhaust housing is expediently equipped with fastener means and/or connector means for producing a connection to other components of the device, such as, for example, a device frame or exhaust air source. The exhaust housing may incorporate guide means such as e.g. baffles, grooves, passages or the like for the air stream flowing in its interior
The chip communicating window extends preferably over substantially the full height of the section of the exhaust housing communicating with the tool cavity. The width of the chip communicating window as measured in the rotational direction of the tool at the outer circumference of the pot section 12 communicating with the tool cavity is selected as a function of the fanout of the chip trajectory as materializing for a particular application. More particularly, it is good practice to select the width smaller than the pitch of the tool cutters. The width of the chip communicating window may be defined either fixed or, however, also variably adjustable e.g. by shifter elements, interchangeable window inserts or the like. The location of the middle of the window relative to the width may be either symmetrical or asymmetrical to the position of the active site of the tool and also manipulated by changing the stationary position of the exhaust housing relative to the active site of the tool. For this purpose suitable adjusting means may be provided.
Preferably the free communicating cross-section of the exhaust passage is reduced in the direction of the exhaust air source.
The auxiliary air infeed opening may be, for example, a drilling, recess or the like porting directly or indirectly into the exhaust passage. The auxiliary air infeed opening may be connected via an auxiliary air passage to the exhaust passage. The opening of the auxiliary air infeed is provided preferably in a portion of the exhaust housing provided outside of the rotating tool. The term xe2x80x9cauxiliary airxe2x80x9d as formulated in the sense of the invention is intended to indicate an air stream flowing through the auxiliary air infeed opening positively influencing another air stream flowing in the exhaust housing, namely an air stream flowing pulsating through the chip receiving opening and the chip communicating window into the exhaust passage due to rotation of the tool and the effect of the exhaust air source, i.e. exerting an auxiliary effect in achieving, in the end, a main air stream having specifically desirable properties in the exhaust passage. This aspect will be detailed later on.
The device in accordance with the invention has the following advantages.
Due to the stationary section of the exhaust housing communicating with the tool cavity, the tool cavity is decoupled from the conditions existing predominantly therein due to rotation of the tool, and other more favorable operating conditions are created.
In the solution in accordance with the invention the section of the exhaust housing protruding into the tool cavity more or less fills the cavity, the inner wall of the cavity being located directly opposite the outer wall of the communicating section of the exhaust housing over an interspace normally only being a minimum, as a result of which no substantial air mass volume exists in the tool cavity which could be exposed to a centrifugal effect caused by rotation of the tool. The interspace between the outer side of the exhaust housing section, radial relative to the axis of rotation of the tool, and the radial inner side of the tool is insufficient for this purpose. The section of the exhaust housing communicating with the tool cavity is arranged stationary and accordingly the cavity of this exhaust housing section is free of all and any centrifugal force effects of the tool rotating about the exhaust housing section, i.e. now, no air stream can build up within this section of the exhaust housing communicating with the tool cavity which flows outwardly to the inner wall of the tool or the chip receiving opening and precisely opposing the direction of movement or natural trajectory of the chips entering the tool.
Thus, a chip parted from the cutter(s) flies, after leaving the chip receiving opening of the tool, over a negligibly small interspace directly through the chip communicating window into the exhaust passage without being influenced by the rotating tool located outside. This is why the movement of the chips into the exhaust passage is neither obstructed nor decelerated or even carried back from the chip receiving opening. This is to be viewed as a major advantage, especially where large chips are concerned. Unlike conventional devices featuring an opposing flow to disadvantage, in the device in accordance with the invention, chip removal is not detrimented whilst effectively avoiding blockage of the chip receiving opening in thus aggravating tool wear. The possibility of chips gaining access from the tool cavity or the exhaust passage back to the outer side of the tool where they are recut by the cutters is also external slight, this likewise contributing to a reduction in tool wear, achieving higher tool life and less pollution of ambient air.
Because in the configuration in accordance with the invention, the chips entering the tool cavity and the exhaust passage are not decelerated, and the interspace between the wall of the tool cavity and the outer wall of the communicating exhaust housing section is small, there is now little probability of chips gaining access to this interspace and being forced by the centrifugal effect of the rotating tool against the inner wall where they accumulate and even form a blockage. This likewise facilitates chip removal and avoids unbalance of the tool due to chips accumulating. This is particularly conducive to the operating safety and accuracy of the tool when operating at high speeds.
Due to the fact that, as a result of the effect as mentioned previously in operation of the device in accordance with the invention, hardly any chips gain access back to the outer side of the tool assigned to the workpiece, chip accumulation or deposits at the surface of the tool as well as the marks resulting therefrom can now be effectively avoided. Recutting of the already separated chips and marks spoiling the appearance of the workpiece as a result thereof, are hardly observed with the device in accordance with the invention, all of which results in an improvement in the useful life and quality of the tool.
It is to be noted at this point that the positive effects of the device in accordance with the invention as explained above can already be achieved by providing the exhaust housing section communicating at least in part with the tool cavity without activation of the exhaust air source being mandatory for this purpose. However, operating the exhaust air source and thus active chip exhaust enhances the advantageous effect of the said exhaust housing section as detailed in the following.
Since the chips, as mentioned above, fly non-decelerated through the chip communicating window into the exhaust passage and have a relatively high kinetic energy, this movement energy can be made use of to discharge the chips. Accordingly, exhausting the chips is thus achievable with low power and low air mass flow which merely needs to be sufficient to transport the chips from the tool to a chip bunker or the like. Even at high cutting speeds or high rotary speeds no particularly high exhaust velocities or high power exhaust means are needed for effective chip removal. This thus enables not only the power requirement but also the noise nuisance caused by the exhaust system to be reduced.
However, the noise emission caused by the tool itself is considerably reduced in using the device in accordance with the invention. Due to the section of the exhaust housing protruding into the tool cavity in connection with the provision of the auxiliary air infeed opening the tool cavity is namely decoupled acoustically to the same degree and both the acoustical and the flow-technical conditions in the tool cavity are positively influenced.
When the exhaust air source is active, a flow of (outside) air usually flows from the outer side of the tool through the chip receiving opening and the chip communicating window into the exhaust passage. Since the hollow tool with its chip receiving opening rotates about the chip communicating window, the path of the flow through the chip communicating window is thus periodically closed and reopened, resulting in (similar to the situation with the prior art tool as mentioned at the outset) a pulsating air stream, which in the absence of some corrective means would generate very loud and extremely unpleasant screeching and/or pulsating acoustical oscillations. In accordance with the invention an auxiliary air flow is made available by means of the auxiliary air flow infeed opening which, within the exhaust passage, is blended with or superimposed by the air stream entering pulsating through the chip communicating window. This results in a substantially constant exhausting main air stream flowing within the exhaust passage along the chip communicating window.
Due to the pulsating air stream being blended or super-imposed with the auxiliary air stream the peaks in the pulsation are reduced or damped in also avoiding resonant-type oscillations in thus enabling noise emission and the extremely unpleasant screeching and/or pulsating acoustical oscillations to be substantially reduced. This high consistency of the main air stream, as compared to a pronounced pulsating air stream, is to be attributed to the fact that air can always be drawn in through the auxiliary air infeed opening even when the chip communicating window is periodically closed, due to tool comprising the chip receiving opening rotating about the chip communicating window.
Since, in addition to this, the main air stream flows along the inner side of the exhaust passage at the chip communicating window and thus allowing no dead space to materialize, any undesirable deposits or accumulations of chips at the rims or edges of the chip communicating window or peaks in the pulsation adjoining thereto are reliably eliminated.
In summary, the device in accordance with the invention thus permits considerable improved chip removal, with the aid of which the chips can be intercepted and discharged to an extremely high percentage whilst significantly reducing the exhaust air and power needed therefor (by as much as approx. 50%) whilst simultaneously reducing the noise emission with its disadvantageous acoustical effects. All these advantages are achieved with relatively little complication and expense in production. The device in accordance with the invention works high effectively in both a technical and cost-effective sense in ensuring high machining quality.
In accordance with one advantageous aspect of the device in accordance with the invention the tool is substantially configured as a pot-type hollow body. This pot-type shape, be it cylindrical, conical, bell-shaped or also regular or irregular shaped, and especially also including a rotationally symmetrical configuration, is particularly of advantage for use in conjunction with the exhaust housing communicating with or protruding at least in part into the tool cavity.
In addition, the part of the exhaust housing communicating with the tool cavity is preferably configured such that it totally fills the cavity substantially. xe2x80x9cSubstantiallyxe2x80x9d in this respect means that a sufficient, preferably small, gap of the interspace always remains between the outer circumference or outer surface areas of the exhaust housing and the inner circumference or inner surface areas of the tool to ensure safe operation of the rotating tool. Arranging for the corresponding tool cavity to be filled practically totally ensures more particularly that the radial distances between the chip receiving opening of the tool and the chip communicating opening of the exhaust housing can be maintained small, and in active operation of the device no large quantities of chips gain access to the tool cavity or between the cavity wall and outer surface areas of the exhaust housing where they could possibly undesirably accumulate or deposit due to the centrifugal effect or force thereof.
Another advantageous aspect of the invention provides for the part of the exhaust housing communicating with the tool cavity being configured pot-shaped in thus enabling this part of the exhaust housing to close off against the tool cavity and, in conjunction with further device features, as detailed later, specifically desirable flow conditions can be achieved in the interior of the exhaust housing. The pot-type section of the exhaust housing may be rotationally symmetrical to the remote portions of the exhaust housing so that for various applications differingly configured pot-type hollow bodies can be interchanged with no undue complication in assembly and disassembly.
In yet another preferred aspect of the device in accordance with the invention, fitted with a tool whose cavity is shaped cylindrical, the part of the exhaust housing communicating with the tool cavity is likewise substantially cylindrical in shape. Furthermore, it is good practice with a device in accordance with the invention fitted with a tool whose cavity is conical, when the part of the exhaust housing communicating with the tool cavity is also configured substantially conical. Both of the variants as aforementioned ensure, for one thing, that in the case of a substantially or totally rotationally symmetrical tool, the outer circumference of the exhaust housing can be adapted to a small interspace in the tool cavity and the distance between the chip receiving opening of the tool and the chip communicating opening of the exhaust housing is in turn to be maintained small. Where a tool is concerned having a conical cavity which assists, on rotation of the tool, removal of the chips having gained access to the tool cavity, the chips can thus be removed through the interspace formed between the inner surface areas of the tool and the conical outer surface areas of the exhaust housing. The tool cavity and the part of the exhaust housing communicating with the tool cavity feature preferably the same degree of conicity, although it is just as conceivable to configure the degree of conicity of these two parts slightly different or even to combine a conical wall of the tool cavity with a cylindrical outer wall of the exhaust housing.
Preferably the exhaust housing comprises a communicating opening or a recess for receiving a drive means, more particularly a shaft or spindle of the rotating tool. Due to the hollow or pot-type configuration of the tool this can be mounted or sleeved onto the exhaust housing to permit achieving a low-profile configuration. The communicating opening or recess is preferably defined by a parting wall or the like relative to other cavities of the exhaust housing, more particularly however relative to the exhaust passage of the exhaust housing.
In accordance with still another advantageous aspect of the device in accordance with the invention, the exhaust passage defines a flow path substantially radial relative to the axis of rotation of the tool which, starting from the auxiliary air infeed opening, guides along the chip communicating window in the direction of the exhaust air source.
The main air stream guided on this radial flow path thus runs substantially in the same direction as the natural trajectory of the chips as gaining access through the chip receiving opening of the tool and chip communicating window into the exhaust passage. As soon as the chips have passed through the chip communicating window, they are relieved of the effect of a centrifugal force existing otherwise in the tool cavity. Since the chips, directly after being generated by the tool, already have a considerable kinetic energy and are neither decelerated nor substantially deflected, their kinetic energy can be made use of directly for discharging the chips. In other words, the chips actively assist, to a certain degree, chip removal of their own accord. Since, in addition, the main air stream flows practically in the same sense as the chip trajectory, only a small amount of kinetic energy of the air mass flow is needed in turn for further chip discharge. This has the result, in all, that the efficiency of chip removal is substantially enhanced whilst enabling the power of the exhaust means or the exhaust air source to be considerably reduced as a whole. Since, in addition, the main air stream flows along the inner side of the exhaust passage at the chip communicating window in thus preventing dead space materializing, any tendency of the chips to accumulate or block the rims and edges of the chip communicating window or in adjoining passage portions is reliably prevented.
Experience has additionally indicated it to be good practice to extend the exhaust passage, starting from the chip communicating window or the auxiliary air infeed opening and relative to the axis of rotation of the tool, substantially radial in the form of a circular arc or spiral about the axis of rotation. Configuring the run of the exhaust passage in the form of a circular arc or spiral in the sense of the invention is also to be understood as a spiral extension of the exhaust passage. The exhaust passage may be guided only in part, substantially completely or even in several windings about the axis of rotation. It is this configuration that in turn permits guidance of the main air stream adapted to the chip trajectory as predominantly natural in the interior of the exhaust housing whilst permitting, in addition, a highly compact and flow-technically favorable configuration of the exhaust housing and exhaust passage, It is for this reason that the chips themselves can be reliably exhausted with less power of the exhaust air source than as required by conventional devices, since it is easy for them to follow the course of the exhaust passage, as described, as well as the flow existing predominantly in the exhaust passage.
In this context, it has been discovered to be good practice to configure the exhaust passage such that the twist direction of the extent of the exhaust passage, in the form of a circular arc or spiral, and the direction of rotation of the tool in the same sense, since for this type of tool the direction of rotation corresponds likewise to the natural chip trajectory in the interior of the tool or exhaust housing.
The exhaust housing comprises preferably at least one ancillary exhaust passage which is connected to the at least one exhaust housing ancillary opening provided at an exhaust housing section located outside of the tool, the ancillary exhaust passage defining a flow path for an ancillary air stream and porting into an exhaust passage section downstream remote from the chip communicating window relative to the exhaust direction into the exhaust passage. With the aid of the ancillary exhaust passage and the exhaust housing ancillary opening, chips occurring outside of the tool or outside of the portion of the exhaust housing communicating with the tool cavity, not gaining access to the tool cavity and/or through the chip communicating window to the exhaust passage, are captured and likewise discharged. Merging the auxiliary air stream and main air stream at an exhaust passage section downstream remote from the chip communicating window relative to the exhaust direction ensures that the auxiliary air stream has no negative effect on the main air stream in the vicinity of the chip communicating window. Since the ancillary exhaust passage ports into the exhaust passage, no separate exhaust air source is needed for operating the ancillary exhaust passage, i.e. instead use being made of the same exhaust air source as put to use for the exhaust passage itself, although, of course, it is basically possible to connect the ancillary exhaust passage to a separate exhaust means or exhaust air source.
For certain applications it has been demonstrated to be good practice to configure the front rim of the chip communicating window, relative to the direction of rotation, substantially recessed or shaped concave. The front window rim is understood to be the rim to which the cutters of the rotating tool run, it having been demonstrated to be good practice that this configuration contributes, among other things, to a further reduction in the noise emission of the tool.
In one particularly advantageous aspect of the device in accordance with the invention it is provided for that the chip communicating window has at least one irregular shaped window rim. In this way, an outside air stream flowing pulsating through the chip communicating window into the exhaust passage of the exhaust housing, due to the rotation of the tool and the effect of the exhaust air source, is swirled at the irregular shaped window rim more or less automatically. At the same time, an air layer entrained by the rotation of the tool in the cavity thereof and flowing along the outer side exhaust housing protruding into the tool cavity, is automatically swirled by the irregular shaped window rim. It has been discovered that the negative acoustical oscillations occurring in conventional devices and tools can be considerable reduced by this constructive detail.
The positive effect, as described above, of the irregular shaped window rim is particularly of advantage when the irregular shaped window rim is configured at a side of the chip communicating window extending transversely to the direction of rotation of the tool. It is to be noted at this point expressly, however, that the irregular shaped window rim is not restricted exclusively to this arrangement, i.e. the other window rims may just as well be shaped irregular. In this case, preference is given more particularly to a variant in which both the front and the rear window rim, relative to the direction of rotation, are shaped irregular.
The irregular shaped window rim as cited above may be achieved, for example, by way of toothed or jagged protuberances and recesses, whereby the protuberances and recesses may be formed regular or irregular and comprise shapes, dimensions and distributions which may be the same or differ over each window rim. In accordance with a further preferred aspect of the device in accordance with the invention the toothed or jagged protuberances and recesses are configured corrugated, although, of course, mixed shapes of the configurations of the irregular shaped window rim as described above are just as conceivable. In addition, the irregular shaped window rims of the chip communicating window may comprise an irregular shape or configuration or, however, similar to or differing from each other.
It has, in addition, been discovered to be an advantage that at least one front window rim, relative to the direction of rotation of the tool, (i.e. the window rim to which the cutters run in operation) of the chip communicating window comprises a chip sweeper, although it is just as possible to provide such sweeper means at the other window rims of the chip communicating window. The chip sweeper may be a separate means or, however, an integral component of the corresponding window rim and/or of the exhaust housing. In the case of it being an integral component, it is especially the window rim of the chip communicating window shaped irregular as described above that may function as such an integral chip sweeper. Movably arranged sweepers with or without their own drive as well as nozzle-type elements jetting a stream of air, gas or liquid are to be appreciated as chip sweepers in the sense of the invention.
Preferably the front window rim comprises a first sweeper edge, radial relative to the axis of rotation, which protrudes beyond the rear window rim radial relative to the radial extension of the rear window rim. When the exhaust housing is shaped cylindrical, for example, and the chip communicating window is provided at a cylindrical outer circumferential surface area of the exhaust housing, then the radial first sweeper edge protrudes beyond the cylindrical diameter. The radial first sweeper edge is configured preferably as an irregular shaped window rim so that the edge or window rim is able to assume a dual function.
In addition to this, it has been discovered to be good practice when the front window rim of the device in accordance with the invention comprises a second sweeper edge axial relative to the axis of rotation of the tool protruding beyond the axial face of the section of the exhaust housing communicating with the tool cavity. This second sweeper edge preferably serves to sweep chips or chip debris through the chip communicating window into the exhaust passage gaining access axial to the outer side of the portion of the exhaust housing communicating with the tool cavity between the inner surface areas of the tool and the outer surface areas of the exhaust housing. The axial second sweeper edge thus reliably removes chip debris which would otherwise undesirably accumulate and become deposited at a section of the tool cavity adjoining the face portion of the exhaust housing.
The sweeper edges as cited above may be configured either sharp edged or blunt and shaped in the form of a cutting edge, blade or even a hook.
In harmony with another aspect of the device in accordance with the invention, the axial face of the section of the exhaust housing communicating with the tool cavity comprises a face closing off this section axially, the face incorporating a face opening porting into the exhaust passage. It is in this face that also the communicating opening or recess for receiving a drive means, such as for example a shaft or spindle of the tool, as described above, may be provided. The closure formed by the face may be configured integrally with the remaining sections of the exhaust housing or releasably configured like a cap, permitting access to the interior of the exhaust housing without requiring disassembly of the complete exhaust housing from the other components of the device. By providing the face and the closure of the exhaust housing configured in this way axially, it is in addition particularly simple to achieve a pot-type shape of the section of the exhaust housing communicating with the tool cavity. This prevents an uncontrolled intake of air at locations of the exhaust housing not intended for this purpose and thus contributes to achieving flow conditions as specifically desirable within the exhaust housing. In turn, this face opening permits exhaust and guidance into the exhaust passage of chips or chip debris possibly gaining access to the face of the exhaust housing or the bottom region of a pot-shaped tool. The interspace between the inner surface areas of the tool and the outer surface areas of the exhaust housing protruding into the tool cavity can thus be maintained free of chips which also reduces wear.
Preferably the face opening ports into the chip communiating window. Chips or chip debris exhausted via the face opening can thus be directly communicated through the chip communicating window into the exhaust passage; and no additional passages and/or an additional exhausting source is needed to exhaust the face opening.
In accordance with still another preferred aspect of the device in accordance with the invention, the face opening in the region of the radial first sweeper edge and/or in the region of the axial second sweeper edge ports into the chip communicating window. Due to the flow passing through the face opening, the effect of the corresponding sweeper edges is thus assisted, and chips or chip debris not captured by the corresponding sweeper edge can thus be captured and discharged due to the flow conditions at the edge of the chip communicating window as induced by the air stream flowing through the face opening.
In one particularly advantageous embodiment of the device in accordance with the invention, it is furthermore provided with an exhaust hood surrounding or enclosing the tool at least in part, or indeed substantially totally in certain applications, as may be achieved in the radial and/or axial direction of the tool. With the aid of the exhaust hood, chips materializing at the outer side or outside of the tool and/or outside of the cutter trajectory and/or outside of the actual exhaust housing can be intercepted which cannot be captured by the exhaust housing communicating with the tool cavity. Relative to the tool or the body thereof it is thus possible in this way to achieve an external chip removal or a kind of external chip guidance.
The exhaust hood may comprise one or more exhaust hood passages, for example in the form of partial passages, several passage sections, grooves, guide means such as for instance baffles and the like, thus making it possible to undertake exhaust simultaneously at different locations as well as to specifically influence chip guidance in directing the chips to specifically desirable locations of the device.
Preferably the exhaust hood is connected to the ancillary exhaust passage of the exhaust housing. This permits the exhaust means or exhaust air source provided for the exhaust housing to also be made use of for operating the exhaust hood, thus eliminating the need for a separate exhaust means or exhaust air source and permitting a very compact configuration of the function unit formed by the exhaust housing and the exhaust hood.
In accordance with still another aspect of the device in accordance with the invention, the exhaust hood juts beyond the tool axially, thus enabling the exhaust hood to also capture chips flung out to a spatial location axially remote from the actual activity site of the tool.
In an additional advantage embodiment of the device in accordance with the invention, it is provided for that the exhaust hood comprises an irregular shaped exhaust hood opening rim. Similar to the irregular shaped window rim of the chip communicating window, as described above, the irregular shaped opening rim of the exhaust hood may likewise comprise toothed or jagged protuberances and recesses or be configured corrugated. The protuberances may in turn be shaped and/or distributed regular or irregular and/or comprise the same or differing configurations and dimensions, although, of course, mixed shapes of the variants as cited above are just as possibility. These means prevent disadvantageous acoustical effects due to the air stream entering through the exhaust hood opening (termed additional air stream in this case) and thus considerably reduce the noise emission generated thereby.
It is more particularly in conjunction with the machining of straight workpiece edges and rims that an aspect of the device in accordance with the invention has produced good results in which the opening rim of the exhaust hood extends substantially tangentially relative to the axis of rotation and a cutter trajectory diameter of the tool from which it is slightly set back in the direction of the axis of rotation. In actual practice the amount of this set-back corresponds to a dimension which is slightly greater than the cutting depth of the tool cutters. This is why in active operation of the device, the opening rim of the exhaust hood extends tangentially directly opposite the straight workpiece edge to be machined over a very small interspace, as a result of which the chips generated at active site of the tool, not gaining access through the chip receiving opening of the tool and through the chip communicating window of the exhaust housing to the exhaust passage, can be excellently captured and discharged to a high degree. The technical problem forming the basis of the invention is furthermore solved by a method in accordance with the invention having the features of claim 29.
This method for machining workpieces, more particularly workpieces of wood-based materials, plastics or the like, by means of a device as set forth in any of the claims 1 to window rim 28 comprises the following steps for exhausting chips materializing in machining:
generating a main air stream flowing substantially constant, exhausting and within the exhaust passage along the chip communicating window.
The method in accordance with the invention offers substantially the same advantages as those of the device in accordance with the invention as already explained above.
In accordance with one preferred, advantageous aspect of the method in accordance with the invention this comprises the step in the method in which the main air stream is directed on a substantially radial flow path, relative to the axis of rotation of the tool, starting from the auxiliary air infeed opening, along the chip communicating window in the direction of the exhaust air source. It is in this way that the main air stream runs substantially in the same direction as the natural trajectory of the chips entering the exhaust passage through the chip communicating window to thus actively assist chip removal to a certain extent. This, in turn, results in the effect of chip removal being enhanced whilst reducing the total power of the exhaust means or exhaust air source as needed for chip discharge. Since the main air stream flows at the inner side of the exhaust passage along the chip communicating window, and thus producing no dead space, this reliably prevents any undesirable deposits or accumulation of chips at the rims or edges of the chip communicating window or portions of the passage adjoining thereto.
In addition, the method in accordance with the invention comprises a variant including a step in the method which is characterized by generating and making available at least one substantially constant exhausting ancillary air stream within the ancillary exhaust passage connected to the ancillary opening of the exhaust housing. Generating and making available the ancillary air stream makes it possible to undertake an additional chip exhaust also at other locations within and/or outside of the section of the exhaust housing communicating with the tool cavity. More particularly, it is possible in this way to also capture chips occurring at an external portion of the tool and not gaining access to the tool cavity and/or through the chip communicating window into the exhaust passage.
In a further preferred step in the method the main air stream and ancillary air stream are merged at a flow section downstream remote from the chip communicating window relative to the exhaust direction. This ensures, for one thing, that the ancillary air stream does not negatively influence the main air stream in the vicinity of the chip communicating window whilst, for another, making it possible in generating and making available the ancillary air stream to make use of, at no additional expense, the means which also find application for generating and making available the main air stream. However, it is basically possible to generate and provide the ancillary air stream also with the aid of separate means.
The method in accordance with the invention offers, in addition, an advantageous variant comprising a step in the method characterized by automatically swirling a stream of outside air flowing pulsating through the chip communicating window into the exhaust passage of the exhaust housing due to rotation of the tool at at least one window rim of the chip communicating window. In this way disadvantageous acoustical oscillations at the chip communicating window can be avoided and the total noise emission of the tool considerably reduced in implementing the method.
More particularly in this case a step in the method in accordance with the invention is also to be viewed as being useful and helpful in which a layer of air entrained due to the rotation of the tool in its cavity and flowing at an outer side of the exhaust housing protruding into the tool cavity and along the chip communicating window is automatically swirled at at least one window rim of the chip communicating window. This too, contributes towards reducing the noise emission.
In yet another advantageous step in the method in accordance with the invention, the pulsating inflowing outside air stream is mixed with the substantially constant main air stream in the exhaust passage. Due to the resulting superimposing effect, peaks in the pulsation of the acoustical oscillations stemming from the pulsating flow condition can be diminished and resonant type oscillation conditions avoided. This in turn contributes towards reducing noise emission and nuisance.
The method in accordance with the invention comprises furthermore an advantageous step in the method which is characterized by generating and making available a substantially constant exhausting additional air stream at an outer side of the tool. This aspect also permits chips materializing at a spatial location outside of the tool and/or outside of the cutter trajectory and/or outside of the exhaust housing and/or at the outer surface areas of the tool itself to be exhausted, not permitting capture by the main air stream, in thus achieving an external chip guidance.
It is to be noted at this point that the invention makes a distinction between an ancillary air stream and an additional air stream, since the ancillary air stream may be an air stream which must not necessarily flow outside of the exhaust housing, whereas the additional air stream is understood to be an air stream which flows at an outer side of the tool and thus, as a rule, also outside of the actual exhaust housing.
However, there are certain circumstances under which the additional air stream may also represent an ancillary air stream or translate into the ancillary air stream. This is e.g. the case when the exhaust hood or at least one of its passages is directly connected to the exhaust housing ancillary opening of an ancillary exhaust passage. When both an additional air stream and an ancillary air stream, separate therefrom, is provided, these two streams may be merged and in this way the chips entrained by them discharged on a common further flow path which facilitates later collection and disposal of the chips. In addition to this, this step in the method offers the possibility of generating the additional air stream with the aid of the ancillary air stream flowing in the ancillary exhaust passage so that separate means for generating the additional air stream can be dispensed with, although it is just as conceivable to provide for a totally separate guidance of the additional air stream and/or separate means for generation thereof.
Preferably the additional air stream is automatically swirled at at least one opening rim of the exhaust hood in avoiding disadvantageous acoustical effects, due to the additional air stream flowing into the exhaust hood opening, and reducing undesirable noise emission.
In conclusion, the method in accordance with the invention also comprises an advantageous step in the method which is characterized by automatically swirling of an air layer entrained due to rotation of the tool at the outer side thereof and flowing along an exhaust hood opening at the at least one exhaust hood opening rim, this too making a positive contribution towards avoiding disadvantageous acoustical effects and reducing noise emission.